Patients who are critically ill or undergoing surgical procedures involving the lungs (thoracic surgery) frequently require a portion of the lung to be isolated from mechanical ventilation. The lungs are located in the chest cavity and bounded by the chest wall and the diaphragm, a thin muscular membrane. The lungs are held next to the chest wall by negative pressure and a thin fluid layer. The space of opposition is the pleural space. The lungs are made of the trachea, an air conduit, and the lung tissue which abuts against the chest wall. The trachea divides in the chest cavity into two separate air conduits, a right sided air conduit (the right mainstem bronchus) and a left sided air conduit (the left mainstem bronchus). The left mainstem bronchus makes a greater angle than the right mainstem bronchus, and the passage of catheters into the left mainstem bronchus is difficult.
Ventilation is a physiologic process which supplies oxygen to the body and removes carbon dioxide, a gaseous waste product. Ventilation is provided by the rhythmic back and forth motion of air in the trachea. Air enters and exits through the mouth connected to the trachea. In health, the rhythmic motion of air is provided by the rhythmic contraction and relaxation of the diaphragm. In surgical patients and the critically ill, ventilation is commonly provided mechanically using a mechanical ventilator and an endotracheal tube. An endotracheal tube is a balloon tipped catheter open at both ends, which is positioned in the mid trachea. It is connected to the mechanical ventilator to provide ventilation.
Isolation of ventilation is required commonly. In thoracic surgery, the chest wall is incised, the lung opened and the pleural space entered. As a result, the lung will collapse, and ventilation can escape. The ventilation to the nonoperative lung must be isolated before opening the operative lung segment. The risk of patient harm exists if ventilation is not isolated before beginning thoracic surgery. This results from the escape of ventilation through the surgical lung opening. Isolation of ventilation is commonly required in medical patients. A portion of the lung can be diseased and requires isolation from mechanical ventilation. Conditions which require isolation are infection of the lung (pneumonia); bleeding in the lungs (hemoptysis); and a non-surgical opening into the pleural space (pneumothorax).
A double lumen endotracheal tube is a commercially available device to achieve isolation of ventilation. A double lumen endotracheal tube is made of two endotracheal tubes fused together of unequal length. It incorporates two balloons, one balloon which envelopes the tracheal position of the two fused endotracheal tubes (the tracheal balloon) and a second which envelopes the longer portion and will extend into either the right or left mainstem bronchus (the bronchial balloon). A double lumen tube will isolate ventilation when positioned correctly with the longer portion in the right or left mainstem bronchus, and both balloons are inflated. There are disadvantages in using double lumen endotracheal tubes. Double lumen endotracheal tubes are larger in diameter and longer than conventional endotracheal tubes and can damage the vocal chords and the nerves for the vocal chords. The left mainstem bronchus is difficult to enter with the longer portion. In patients where the normal airway anatomy is altered, the use of double lumen endotracheal tubes has caused patient harm. Due to the complexity and size, hypoxic brain damage has occurred because of the time needed to correctly place the device in the airway. A double lumen endotracheal tube can not be left in place for long periods of time. Due to its size, it can cause damage of the tracheal bronchial tree including disruption.
An endobronchial blocker is another device to achieve isolation of ventilation. An endobronchial blocker is a balloon tipped catheter, which is placed using a fiberoptic bronchoscope. The balloon is positioned in either the right or left mainstem bronchus. The balloon is inflated to achieve isolation of ventilation. A commercially available vascular, balloon-tipped catheter is used routinely for an endobronchial blocker to achieve endobronchial blockade. The vascular, balloon-tipped catheter has disadvantages. The vascular, balloon-tipped catheter is not coupled to the motion of the fiberoptic bronchoscope. The fiberoptic bronchoscope is used only to view the vascular, balloon-tipped catheter when positioning the catheter. The operation of the fiberoptic bronchoscope and vascular, balloon-tipped catheter are entirely independent. The vascular, balloon-tipped catheter is very difficult to place in the left mainstem bronchus. It routinely requires several attempts to position correctly. The vascular, balloon-tipped catheter uses a removable stiff mandrel wire, placed in the catheter lumen, to allow manipulation during placement. This can cause tissue trauma due to the stiffness of the end portion. The vascular, balloon-tipped catheter incorporates only a single lumen in the design. This lumen accepts the removable mandrel wire and allows inflation of the balloon with the mandrel wire removed. The single lumen does not allow gas to be aspirated from the blocked section, gas to be added to the blocked section, irrigation fluid to be added to the blocked section, and irrigation fluid, secretions or blood to be removed from the blocked section. The balloon of the vascular, balloon-tipped catheter is not optimal. The inflated balloon is spherical in shape allowing easy dislodgement. The balloon is of a low volume, low compliance, high pressure, spherical type designed to be filled with fluid to remove blood clots from blood vessels. This type of balloon can transmit excessive pressure to the tracheal wall causing damage. The balloon has no mechanism to sense the inflation pressure.
A Univent tube is another commercially available device to achieve isolation of ventilation. A Univent tube is an endotracheal tube designed with a large lumen and a small lumen. The large lumen allows ventilation using conventional means. The smaller lumen accepts an endobronchial blocker. The endobronchial blocker is advanced into the right or left mainstem bronchus, and the balloon is inflated to achieve isolation of ventilation. The remaining portion of the Univent tube remains in the trachea in the same fashion as a conventional endotracheal tube.
The Univent tube has disadvantages. The endobronchial blocker can be difficult to place in the left mainstem bronchus. It should be placed using a fiberoptic bronchoscope. The motion of the fiberoptic bronchoscope and the blocker are entirely independent. In clinical practice, the Univent tube is larger in diameter than a conventional endotracheal tube. This can lead to difficulty in placement and damage to the vocal chord mechanism. The ventilation lumen of the Univent tube is smaller in cross-sectional than that of a similar sized conventional endotracheal tube. In patients with severe pulmonary disease, this smaller cross-sectional area can make removal of the Univent tube at the conclusion of surgery difficult. The work of breathing through this small lumen is higher and there is the risk of ventilatory failure.